The overall goal of this research program is to determine where in the brain the barbiturates act to cause each of their various effects and to determine the mechanism(s) by which these effects are elicited. The present proposal focuses on the anesthetic and anxiolytic effects of barbiturates. The drugs will be administered to awake, freely moving rats via chronically implanted cannulae directed to specific brain sites. Anesthesia will be evaluated as loss of the righting reflex and loss of responsiveness to external stimuli. Antianxiety effects will be measured as an increase in punished responding in the Geller-Seifter paradigm. When the brain sites for these effects are found the mechanism of barbiturate action at these sites will be evaluated in several ways. For example, in vivo the GABAergic nature of the effects will be assessed by comparing the effects of other GABAergic drugs and by determining if the effect of barbiturates can be reversed by GABA antagonists or local GABA depletion. In vitro the effects of barbiturates on the binding of ligands for GABA sites (3H-GABA), benzodiazepine sites (3H-flunitrazepan) and the chloride ionophore (35S-TBPS) will be determined under conditions as close as possible to physiological. The effects of barbiturates on radioligan binding will be correlated with the in vivo effects. Whether or not tolerance to the anxiolytic effect develops as it does to the anesthetic effect will be determined, and the possibility that alterations in the binding sites or effects of barbiturates on them can explain the development of tolerance to either or both of these effects will be tested.